Collaborative Research: Emergent Mechanics of Randomly Packed Elastic Filaments

合作研究：随机填充弹性丝的新兴力学

• 批准号: 1825924
• 负责人: Hunter King
• 金额: $ 26.3万
• 依托单位: University of Akron
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-09-01 至 2022-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1825924&HistoricalAwards=false
• 关键词: Collaborative; Research; Emergent; Mechanics; Randomly

When a cardinal builds her iconic cup-nest, she uses her own body as template and molds thin twigs, grass strands, and bark strips into a structure that, despite its softness, reliably holds its shape against various mechanical perturbations. This naturally-selected engineering solution is the result of a subtle interplay between geometry, elasticity, and friction that has not yet been characterized or modeled despite its potential in building, packaging, self-repairing, shock-absorption, and material reusability. The 'bird nest', if defined as a random packing of slender, elastic elements, is an unusual material: it is cohesive without attractive interactions; it is collectively soft and plastic while its elements are hard and elastic. Through coordinated physical and computational experiments, this collaborative project will advance the science of soft granular materials by relating bulk mechanical properties of idealized 'nest systems' with variations in constituents' properties and geometry. Results will generate new knowledge in granular physics, and will appeal to emerging aleatory architecture and engineering paradigms. Indeed, the ability to build through impermanent contacts and design lightweight materials with prescriptive mechanical properties cuts through many areas of high current importance: civil engineering and architectures (reliable, inexpensive, reusable and self-repairing materials), transportation (lightweight composites, shock absorbers), advanced manufacturing. This is in line with the national need of increasing industry competitiveness, which advances the national health, prosperity, and welfare; and secures the national defense. The project also promises to capture the imagination of a broad audience by creating an unusual bridge between relatable protagonists (birds) and often inaccessible fields of physics and engineering. Additionally, STEM outreach activities will be conducted at individual institutions to attract middle school students and female students, respectively, towards science and engineering. Undergraduate students will also be offered positions in either group for exposure to advance engineering research.With increasing aspect ratio, the mechanical behavior of disordered granular packings changes. Where applied stresses distribute in chains of 1D contacts for spheroids, slenderness introduces bending moments and long-range interaction. Impermanent frictional contacts set the system apart from semi-flexible polymer networks and other non-woven materials which derive mechanical response from permanent crosslinks. Experimental evidence from disordered, randomly packed, elastic fibers or filaments based structures, such as the bird nests, suggest that these material systems exhibit frequency-dependent elastoplastic behavior, finite tensile response, and enhanced specific strength. In the absence of a theoretical framework and strictly applicable principles of statistical mechanics, an experimental platform for the benchmarking and physical characterization of these materials will be developed in this project. These will be complemented by a high fidelity computational counterpart to direct a search for novel mechanical states and transitions. The project will provide insights into the relationship between macroscopic and microscopic mechanics of bird nest-like systems, paving the way towards prescriptive design of novel materials. Moreover, it will spur new directions in granular physics theory and explain a functional mechanism from a naturally-selected engineered structure.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

当红衣主教建立自己的标志性杯子纽约时，她将自己的身体用作模板，并使细小的树枝，草丛和树皮条塑造成这种结构，尽管它柔软，但它可靠地将其形状固定在各种机械扰动上。这种自然选择的工程解决方案是几何，弹性和摩擦力之间微妙的相互作用的结果，尽管它具有建筑，包装，自我重新培养，减震功能和物质可重复性的潜力，但尚未表征或建模。如果将“鸟巢”定义为细长的弹性元素的随机堆积，则是一种不寻常的材料：它具有凝聚力，而没有吸引人的相互作用；它集体柔软和塑料，而其元素则是坚硬和弹性的。 通过协调的物理和计算实验，该协作项目将通过将理想化的“嵌套系统”的批量机械性能与成分特性和几何形状的变化联系起来，从而推动软颗粒材料的科学。结果将在粒状物理学上产生新知识，并将吸引新兴的核心建筑和工程范式。的确，通过无常接触和设计具有规定的机械性能的轻量级材料的能力削减了许多当前重要性的领域：土木工程和建筑（可靠，廉价，可重复使用和自我修复材料），运输（轻量级复合材料，减震器，减震器），高级制造。这符合全国性的行业竞争力的需求，这可以提高国家健康，繁荣和福利；并确保国防。该项目还有望通过在相关主角（鸟类）和通常无法访问的物理和工程领域之间创建一个异常的桥梁来捕捉广泛受众的想象。此外，STEM外展活动还将在各个机构进行，以分别吸引中学生和女学生攻读科学和工程。本科生还将在任一组中的职位，以接触高级工程研究。随着纵横比的增加，颗粒状包装的机械行为发生了变化。如果施加应力分布在球体的1D接触链中，则细长性引入弯矩和远距离相互作用。无常的摩擦接触使该系统与半灵性聚合物网络和其他非编织材料区分开来，这些材料从永久性交联。来自无序，随机包装，弹性纤维或基于细丝的结构（例如鸟巢）的实验证据表明，这些材料系统表现出频率依赖性的弹性塑性行为，有限的拉伸响应和增强的特定强度。 在没有理论框架和统计力学的严格适用原理的情况下，将在本项目中开发出一个实验平台，用于对这些材料进行基准测试和物理表征。 这些将由高保真计算对应物进行补充，以指导搜索新型的机械状态和过渡。该项目将提供有关类似鸟巢系统的宏观和微观力学之间关系的见解，为新颖材料的规定设计铺平了道路。 此外，它将刺激粒状物理学理论的新方向，并解释一种自然选择的工程结构的功能机制。该奖项反映了NSF的法定任务，并被认为是值得通过基金会的知识分子和更广泛影响的评估来评估的支持标准。

项目成果

Mechanics of randomly packed filaments—The “bird nest” as meta-material

随机排列的细丝的力学——作为超材料的“鸟巢”

• DOI: 10.1063/1.5132809
• 发表时间: 2020
• 期刊: Journal of Applied Physics
• 影响因子: 3.2
• 作者: Weiner, N.;Bhosale, Y.;Gazzola, M.;King, H.
• 通讯作者: King, H.

Micromechanical Origin of Plasticity and Hysteresis in Nestlike Packings

巢状填料塑性和滞后的微机械起源

• DOI: 10.1103/physrevlett.128.198003
• 发表时间: 2022
• 期刊: Physical Review Letters
• 影响因子: 8.6
• 作者: Bhosale, Yashraj;Weiner, Nicholas;Butler, Alex;Kim, Seung Hyun;Gazzola, Mattia;King, Hunter
• 通讯作者: King, Hunter